The spin doctor is in

BY JIM KEOGH

Holy Cross Prof. Matt Koss has led research on "spin decay." Red Sox fans can recount certain homeruns from the team's history as though we're quoting from a sacred text. We unfurl the scrolls to find John Updike's account of Ted Williams' homer in his final at-bat in a Boston uniform. We go to the tape to revisit Carlton Fisk's winning clout in the 11th inning off the 1975 World Series and the sight of Pudge urging the ball to stay fair. And we employ old-world oral traditions to recreate for our children the horror watching Bucky Dent's pop-fly sneak over the Green Monster to beat the Sox in the 1978 playoff against the Yankees.

Holy Cross physics professor and diehard Sox fan Matt Koss enjoys homeruns as much as anyone … with an exception. While he can appreciate the aesthetics of a ball leaving the ballpark — whether it's a laser-shot or lazy parabola — Koss is also intrigued by the mechanics of the sphere's flight. As a scientist, he wants to know what forces are exerting themselves on that ball to both propel and impede its journey.

Kevin Sullo (l.) and Tom Booth get acclimated to the atmosphere at zero gravity. Some might consider his interest a borderline obsession. If so, then he's infected his students.

Over the past year, Koss and HC juniors Tom Booth and Kevin Sullo have been conducting experiments to measure "spin decay" on a hit or thrown baseball. Spin (or rotation) decay denotes the gradual reduction in the number of rotations on a ball as it travels through the air. The rate and type of rotation determines the curve on a ball, and also contributes to how far it will travel.

As Koss explains it, many factors influence the flight of a ball — gravity, air drag, humidity, and something called "Magnus force," which helps determine the curve of the ball's path. (There are other extenuating circumstances, of course. How cleanly the ball was struck, the arm slot of the pitcher, and whether the batter/pitcher was juiced on steroids, but those constitute an entirely different batch of research.)

"A lot of physicists have explored the many subtle mysteries and unknowns [of baseball], but it surprised us that nobody measured how quickly a baseball rotation changes, how it slows down over time," Koss says.

Through their spring semester, Booth and Sullo fired baseballs into the air from a pitching machine and using high-speed photograph and computer models they were able to measure the number of rotations that a ball lost during the course of its flight.

Koss notes a long history of speculation about the rotation rate of a baseball that is hit for a homerun, with some researchers believing the ball's rate of spin will decrease by more than half in over five seconds.

To get a true read on how much a ball's rotation will drop, Koss' students needed a setting where those pesky external forces, like gravity and wind, could be eliminated. They found what they were looking for racing thousands of feet above the earth's surface.

Through an involved application process, which included a formal presentation of their work at MIT, Booth and Sullo were able to snag a ride aboard a specialized jet that reaches speeds of such magnitude the cabin is reduced to zero-gravity. Not only was it an honor to be granted access to the jet — Booth and Sullo were the only undergrads and the only non-MIT students on board — but it gave the students the purest conditions in which to conduct their spin-decay experiments.

On June 21, the students took off from Titusville, Fla. in a modified Boeing 727, their feet strapped to the floor so that they wouldn't float through the cabin. It took a trial run just to get themselves acclimated to their zero-gravity buoyancy, and then they went to work. By using a drill they'd outfitted with a funnel, they were able to fire a baseball eight times and record the number of rotations through high-speed photos.

Unfortunately, the flight organizers had insisted the students propel the ball toward a box fashioned with PVC pipe and netting (their fear was that a loose ball would bonk one of the other researchers on the plane). The times that the ball actually hit the box negated their findings. But in those instances when the ball remained suspended in the air, they were able to obtain usable data.

Their findings: At 6.5 seconds a ball will be rotating about half as many times as when it was released.

Your question: So what?

Well, for right now, the practical applications are for stat geeks only. By plugging a ball's rotation into the other factors affecting its path, scientists, and, eventually, fans will be better able to determine how far, fast and with what kind of curving motion that ball will travel.

Knowing the rotation rate — which affects line drives more acutely than fly balls — in concert with other factors would help determine whether a batted ball is a home run, will hit the wall, will be caught by an outfielder or land in front of him.

Koss, who came of age as a Red Sox fan in the Impossible Dream season of 1967, says the information ultimately could help teams perfect their games.

"If we better understand the physics of baseball, we can created a simulation so accurate that pitching coaches could design game plans based on what a pitcher can do under what conditions; even develop new pitches.

Thirty years ago, nobody knew anything about 'money ball,' only fans were keeping such detail statistic. They discovered things about the way baseball works statistically. Now, general managers use it in scouting and game planning. The same could be true of physics. Maybe there will be a time when each team needs its own physicist for pitchers and hitters."

Wishful thinking. Perhaps it's too late for Prof. Koss, but Booth can allow himself to dream.

"I've always been a fan of the game, though I was never any good at it," he says. "Ideally I'd like to do something with science and sports." He notes that UMass Lowell has a program focusing on major league bats, especially the bat-and-ball collision. Sounds like a topic that cries for further study.